This invention relates generally to dental implants and more particularly to a dental implant having an improved configuration for reducing interproximal bone resorption compared with known implants.
Artificial dental implants, usually made of metal or ceramic, can be used in place of natural teeth to provide a base/support on which an artificial tooth can be fabricated. An artificial dental implant is implanted in the hard tissue (bone) of a patient (referred to as implant). The implant is composed of a machined/polished collar (coronal part) (referred to as collar) and an apical surface characterized by macroscopic and microscopic surface features (referred to as root). A mounting part (abutment) is attached to the implant (referred to as post) to which an artificial tooth (referred to as prosthesis; i.e. crown, denture etc.) can be attached.
Artificial dental implants of the type to which this invention relates can be made from metals, such as titanium and titanium alloys, as well as ceramics such as zirconia based, alumina-based, and sapphire based ceramics.
Of these materials, titanium and its alloys are the most widely used because of their fracture and fatigue resistance, corrosion resistance and biocompatibility.
While osseointegration can be obtained with different types of dental implants, it is common to observe bone loss around the implant in the first year of implant life. Bone loss up to 1 mm is considered to be acceptable in the first year, and bone loss no more than 0.1-0.2 mm is acceptable in subsequent years. Usually, after some initial bone loss, bone levels near the top of the implant (crestal bone level at the coronal macro-microscopic features) reaching a steady state and no significant further bone loss occurs.
A number of explanations for the greater bone loss in the first year after implantation have been proposed. Among these are remodeling of the bone crest due to mechanical loading of the implant, crestal remodeling due to abutment micro movement, crestal remodeling due to contact of polished and/or machined surface of the implant with bone, and resorption of the bone crest due to the presence of inflammatory infiltrate at the level of the implant-abutment junction, possibly caused by bacterial colonization of the inner surfaces of the implant.
Implants are generally cylindrical or modifications of cylindrical in form. The artificial tooth mounting surface (referred to as implant-abutment interface) is normally flat and arranged at an angle perpendicular to the long axis of the cylindrical implant. Conventionally, a machined and/or polished metal collar is immediately adjacent (in the apical direction) the artificial tooth mounting surface. In other words, the machined/polished collar is the most coronal portion of the implant (not considering the antirotational features that may be present at the implant-abutment interface) The collar may have a width of up to a few millimeters, depending on design choices made by the manufacturer.
The root of the dental implant can be threaded, serrated, or lack macroscopic surface features (press-fit design). At a microscopic level, some implant designs include surface modifications such as coating, etching, and grit-blasting to improve osseointegration.
Human tissues, including soft tissues (gums or gingiva) and hard tissues (bone), react differently to the different surfaces. Epithelial tissue (gum) can establish a stable attachment with the machined/polished collar. This attachment forms a seal against bacterial invasion of the underlying hard tissue (bone). Hard tissue that comes in contact with a machined or polished surface such as the surface of the collar is normally resorbed. Resorption normally progresses to and stop at the most coronal macro/microscopic surface features. Therefore, a longer polished/machined collar in contact with bone, leads to greater resorption.
In a healthy patient, the outline of the alveolar bone crest is curved. The outline follows the concavities and convexities of the cemento-enamel junction of the healthy tooth.
The free gingiva, junctional epithelium and connective tissue attachment to the tooth are the most coronal portion of the periodontum (tooth supporting apparatus). The apico-coronal dimension of the junctional epithelium and the connective tissue attachment are together defined as the biologic width. In healthy patients, the apico-coronal dimension of the biologic width is generally constant for different teeth, different individuals, and different ages. This dimension is also recreated during the healing process following periodontal surgery. Therefore, the dimension of the soft tissue (gums of gingiva) is generally constant. The dimension of the biologic width around dental implants and healthy natural teeth is similar. Moreover, different types of dental implants show similar biologic width dimensions.
Studies of implants several years after insertion show that resorption proceeds until the bone crest is at the level of the most coronal macroscopic feature (the first thread for a machined threaded design or serration) or to the level of the most coronal part of the surface microscopic features (coating, etching, and grit-blasted surface). Since, heretofore, the macroscopic and microscopic features lie in a flat line perpendicular to the long axis of the implant, bone loss proceeds to the same level all the way around the implant, including the mesial, buccal, distal, and lingual surfaces. Because the bone level around a natural tooth is not flat, more resorption of the interproximal bone peak occurs than of the buccal and lingual portions. The loss of bone, particularly of the interproximal bone peak, often leads to apical migration of the overlying soft tissues (that have constant dimension: biologic width), including the connective tissue and epithelium, with a resultant gingival recession. This loss is particularly accentuated in the interproximal areas, that are the sides that face another tooth or implant, and is particularly severe when two implants are placed side by side. Gingival recession can lead to an unsightly gap between an implant-supported artificial tooth and an adjacent natural tooth or another implant-supported artificial tooth.
It is an object of this invention to provide an improved dental implant that decreases or eliminates interproximal bone loss by providing an implant that has a coronal part that is curved or angled to correspond to or imitate the cemento-enamel junction of a natural tooth.
It is another object of this invention to provide a dental implant having a polished and/or machined collar and macro/microscopic surface feature that are more coronally extended in the interproximal areas of the implant as mounted in a patient.
It is yet another aspect of this invention to provide an implant having a curved or otherwise angled outline of the coronal machined/polished metal collar that also follows the outline of the cemento-enamel junction and the alveolar bone crest.
It is still another aspect of this invention to provide a dental implant having macroscopic and microscopic surface features that follow the outline of the machined collar.